Various disadvantages of steel

Advantages of a steel I beams and steel columns

There are various disadvantages of Steel, it is known as one of the most common materials used to make I-beams due to its ability to withstand very heavy loads. The steel I-beam posses a strong central core which is capped with flanges on either side various lengths of beam are available which would be appropriate for the construction projects needs. Steel I-beams also carry a rating which indicates how large it is and how much weight it is able to bear they also have a great advantage over wood because it is more unlikely to bend or warp and this allows builders to use steel I-beams to create large open spaces which would not work out with wood. steel I-beam do not need to be as large as a wood made beams because they are of better quality and can withstand more, hereby meaning that the supporting beams in a structure do not need to be so obtrusive. Other advantages of steel include:

Environmental friendly issue

Cost efficiency

Energy Efficiency

Time saving

Steel possesses the highest strength-to-weight ratio of any building material being used today.

Energy Efficiency

Steel framed buildings can be very energy efficient. The strength of steel requires fewer wall studs, so there are fewer thermal bridges which would transmit the heat. Steel frame buildings do not settle or warp up like wood so they remain more airtight and structurally firm. The depth provided by the steel beams gives room for a wider insulation space. The design flexibility of steel framed buildings enables to architects to focus on energy-efficient housing features. Steel cannot rot because it is immune against termites and insects. In the event of a fire steel would not allow the spread of this fire. This is the same is similar disasters like tornados or hurricanes. Also, there is less likelihood of damage from lightning strikes due to superior earthling characteristics of steel. It saves money because Steel doesn't have to be treated with pesticides, preservatives or glues therefore steel framed houses offer indoor air quality benefits.

Disadvantages of a steel I beam and columns

In terms of construction, the labour required is more expensive since welders or skilled workers are needed. If you use concrete, you can hire normal labourers to tie, rebar and place the concrete which is much less expensive. Also many factories are set up to make normal plates and w-shapes as there major so if you want something distinctive you have to pay. Concrete on the other hand, can be cast into any shape you want. The higher the strength of the steel encourages the use of rather shallow members, which causes greater deflections since the deflection is always dependant on the EI term, where I decreases greatly as the depth decreases since it is dependant on the square of the distance from the centroid of the beam to the centroid of the flanges. Weight may be one possibility (steel usually takes less volume for beams and column which could always be lighter than concrete), another may be corrosion. Type of steel used is very pertinent. Some types of steel like passive stainless steel are much more resistant to corrosive effects of air, moisture, acids, salts and electrolytes while retaining the strength steel is known for. If not when using steel it needs to protected either painting or electrolysis. From an ecological green perspective, the total environmental cost of steel can be high, especially with the mild steels or plain galvanized steel. The environmental cost includes the cost of raw processing, manufacturing, installation, maintenance, and re-cycling and replacement costs. Durability and longevity factor in greatly as does the initial mining and processing cost. Stainless can have very long life and is very durable and resistant to stress, in the right environment. Steel has high initial processing costs and can also be high maintenance for types other than stainless.

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The strength of concrete in compression is at least ten times as great as its strength in tension, and by using a material such as steel to take the tensile stresses induced by bending, full advantage can be taken of the high compressive strength of the concrete. A simple beam can be constructed by placing steel bars in a wooden or steel mould and ramming or vibrating in the wet concrete so that it completely surrounds the bars.

On setting and hardening, the concrete shrinks slightly and grips the steel bars firmly, so that when the beam is loaded the steel and concrete bend as one unit, there being no slip (in correct design this is known as bond) between them. (Tendency to slip is due to horizontal shear.) Ordinary mild steel is allowed to take a maximum tensile stress of 275 N/mm2. High yield steel a maximum tensile stress of 460 N/mm2 and the accompanying elongation of the steel, although very small, is sufficient to crack the concrete in the tension zone of the beam. (Since the elongation of the steel is so small, these minute cracks are normally not detectable by eye.)

The cracking of the concrete, which causes the steel to take all the tension below the neutral layer, may be explained in this way. The elastic modulus (E) of steel is about 15 times that of concrete. But concrete fails in tension at a very low stress, the exact figure depending on the quality of the concrete. It follows, therefore, that the concrete below the neutral axis fails in tension and is ineffective for resisting bending stress (although it is still capable of resisting shear forces). In a simple reinforced-concrete beam, the compressive stresses are taken by the concrete and the tensile stresses are taken by the steel.

The position of the neutral layer depends among other factors on the amount of the reinforcement. The resistance of a beam to bending can be varied by varying the amount of steel (and also the proportion of cement to aggregates.

If for a particular mix the percentage of steel is increased further, no advantage results because the concrete in compression will be unable to supply enough resistance to balance the high tension the steel can supply. The strength of the beam can be increased further, however, by placing steel in the compression zone of the beam to help the concrete, although this is not normally economical. It is a method adopted when it is required to keep the beam dimensions as small as possible. Precast concrete COLUMNS may be solid or hollow. If the hollow type is desired, heavy card-board tubing should be used to form the core. A looped rod is cast in the column footing and projects upward into the hollow core to help hold the column upright. An opening should be left in the side of the column so that the column core can be filled with grout. This causes the looped rod to become embedded to form an anchor. The opening is dry packedconstruction and installation of VCC's is a very quiet process with minimal vibration, which dependant upon soil conditions, can permit installation relatively close to existing structures (up to 1.5m in some instances)

Generally no spoil is generated due to the displacement system which is an advantage, especially on contaminated sites

The installation technique is a fast operation with typical production rates in the order of 200 to 300 linear metres per daily shift (dependent upon soil conditions).

The VCC technique permits a quick, simple and cost effective foundation sub-structure over a range of soft/weak soils. In the past, the usual recourse in such soils would have been to adopt a more expensive piled sub-structure

Disadvantages of concrete reinforced beams and columns

Reinforced concrete can fail due to inadequate strength, leading to mechanical failure, or due to a reduction in its durability. Corrosion and freeze/thaw cycles may damage poorly designed or constructed reinforced concrete. When rebar corrodes, the oxidation products (rust) expand and tends to flake, cracking the concrete and unbonding the rebar from the concrete. Typical mechanisms leading to durability problems are discussed below. Reinforced concrete can be considered to have failed when significant cracks occur. Cracking of the concrete section can not be prevented; however, the size of the cracks can be limited and controlled by reinforcement. Cracking defects can allow moisture to penetrate and corrode the reinforcement. This is a serviceability failure in limit state design. Cracking is normally the result of an inadequate quantity of rebar, or rebar spaced at too great a distance. The concrete then cracks either under excess loading, or due to internal effects such as early thermal shrinkage when it cures.

Ultimate failure leading to collapse can be caused by crushing of the concrete matrix, when stresses exceed its strength; by yielding of the rebar; or by bond failure between the concrete and the rebar. ? Adverse environments or poor construction practice can lead to corrosion of the reinforcing steel in concrete.

Ultimate failure leading to collapse can be caused by crushing of the concrete matrix, when stresses exceed its strength; by yielding of the rebar; or by bond failure between the concrete and the rebar